[Xorp-users] Multicast problems

[Pavlin Radoslavov]

> I have a very simple network here (as I don't have enough machines to
> make a more complicated one!).
> 
> Source
>      |
> Router
>      |
> Client
> 
> 
> Source and Router are running XORP - they are neighbors in show pim
> neighbors and seem to be exchanging information fine (holding RP
> elections, etc)
> 
> Source is sending traffic out to a multicast address, and that traffic
> can be seen at Router (on the interface connected to Source).
> 
> 
> Client joins the group (using a c program), and Router sees the join:
> 
> [ 2006/04/01 16:19:52 TRACE xorp_igmp MLD6IGMP ] RX
> IGMP_V2_MEMBERSHIP_REPORT from 10.0.0.30 to 229.9.9.9 on vif eth2
> [ 2006/04/01 16:19:52 TRACE xorp_pimsm4 PIM ] Add membership for
> (0.0.0.0, 229.9.9.9) on vif eth2
> [ 2006/04/01 16:19:52 TRACE xorp_pimsm4 PIM ] Add MFC entry:
> (10.0.0.121, 229.9.9.9) iif = 1 olist = O.O olist_disable_wrongvif =
> .O.
> [ 2006/04/01 16:19:54 TRACE xorp_igmp MLD6IGMP ] RX
> IGMP_V2_MEMBERSHIP_REPORT from 10.0.0.30 to 229.9.9.9 on vif eth2
> 
> However, Router doesn't start forwarding the traffic from Source to
> 229.9.9.9 to Client.
> It still comes in, but doesn't get forwarded anywhere.

Two generic potential problems (they should go into the FAQ):

1. Check the TTL of the multicast data traffic at the sender is
   large enough. By default, the TTL is 1 and packets with such TTL
   won't be forwarded.

2. Check that there are no firewall rules in the Router that prevent
   it from forwarding the multicast data packes.


> What's that stuff about "disable_wrongvif", by the way?

This is to disable the "IGMPMSG_WRONGVIF" kernel signal on
particular interfaces, but it is no-op on Linux. See multicast(4) on
a recent BSD system for details. E.g.:
http://www.freebsd.org/cgi/man.cgi?query=multicast&apropos=0&sektion=0&manpath=FreeBSD+6.0-RELEASE+and+Ports&format=html

Pavlin